The Caliciviridae are a family of positive-strand RNA viruses and consist of four genera designated: (1) Norovirus (with species Norwalk virus); (2) Sapovirus (with species Sapporo virus); (3) Vesivirus (with species, feline calicivirus and vesicular exanthema of swine virus); and (4) Lagovirus (with species rabbit hemorrhagic disease virus and European brown hare syndrome virus). Norwalk virus is the prototype strain for the genus Norovirus and was discovered by LID researchers in 1972. The noroviruses are the major cause of nonbacterial epidemic gastroenteritis that occurs in family, school, institutional, or community-wide outbreaks, affecting all age groups. The human noroviruses are genetically diverse and cannot be grown in cell culture, which has been a continuing research obstacle. [unreadable] A major goal of this laboratory is the development of control strategies for the caliciviruses (predominantly the noroviruses) associated with gastroenteritis. In order to accomplish this goal, basic knowledge of the epidemiology, immunology, and replication strategies of these viruses is needed. In collaboration with researchers at Johns Hopkins University, we characterized a norovirus strain representing a new, emerging GII.4 variant. The gene encoding the capsid protein, VP1, of this virus (designated JHH3) was cloned into a recombinant baculovirus and virus-like particles (VLPs) were produced. We are presently studying the antigenic characteristics of this variant, which may give insight into the selection of a norovirus vaccine candidate. Our work this year focused also on the continued development of murine norovirus as a model because it is the only member of the genus Norovirus that grows in cell culture. Progress was made in localizing the distribution of viral proteins in murine norovirus-infected cells. Last year, with Jerrold Ward, we discovered a new murine norovirus strain in NIH laboratory mice, and this year, several additional murine norovirus strains were discovered and characterized. We continued studies of Norwalk virus in chimpanzees with Dr. Purcell, and developed new methods to quantitate the number of Norwalk virus genome copies shed in chimpanzee stool. Intestinal biopsies were obtained from a chimpanzee shown to be infected with Norwalk virus, and viral RNA was detected in the jejunum. Studies are in progress to further localize the site of virus replication and to examine the effect of Norwalk virus infection on host cell gene expression. This animal model offers a promising alternative to human volunteer studies in the initial development and testing of norovirus vaccine candidates.